U.S. patent number 11,352,923 [Application Number 16/754,623] was granted by the patent office on 2022-06-07 for system and method to mitigate sensor failures due to water condensation.
This patent grant is currently assigned to CUMMINS INC.. The grantee listed for this patent is Cummins Inc.. Invention is credited to Neal W. Currier, Saurabh Y. Joshi, Ashok Kumar, Tyler A. Rash, Anand Srinivasan, Yadan Tang, Di Wang, Aleksey Yezerets.
United States Patent |
11,352,923 |
Joshi , et al. |
June 7, 2022 |
System and method to mitigate sensor failures due to water
condensation
Abstract
A diagnostic system (10) is provided and includes a sensor (24)
disposed downstream from an exhaust gas aftertreatment system. Also
included in the diagnostic system (10) is a central diagnostic unit
(35) configured to diagnose a condensation condition associated
with the sensor (24) for mitigating a sensor failure due to water
condensation on the sensor (24), the central diagnostic unit (35)
performing the diagnosis on the condensation condition based on
water storage and release information related to a component of the
exhaust gas aftertreatment system. The sensor (24) is activated
based on the water storage and release information.
Inventors: |
Joshi; Saurabh Y.
(Indianapolis, IN), Currier; Neal W. (Columbus, IN),
Yezerets; Aleksey (Columbus, IN), Kumar; Ashok
(Columbus, IN), Rash; Tyler A. (Columbus, IN),
Srinivasan; Anand (Greenwood, IN), Wang; Di (Columbus,
IN), Tang; Yadan (Columbus, IN) |
Applicant: |
Name |
City |
State |
Country |
Type |
Cummins Inc. |
Columbus |
IN |
US |
|
|
Assignee: |
CUMMINS INC. (Columbus,
IN)
|
Family
ID: |
1000006353530 |
Appl.
No.: |
16/754,623 |
Filed: |
October 10, 2017 |
PCT
Filed: |
October 10, 2017 |
PCT No.: |
PCT/IB2017/056259 |
371(c)(1),(2),(4) Date: |
April 08, 2020 |
PCT
Pub. No.: |
WO2019/073280 |
PCT
Pub. Date: |
April 18, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200264147 A1 |
Aug 20, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N
3/2066 (20130101); F01N 3/0814 (20130101); F01N
2560/026 (20130101); F01N 2560/028 (20130101); F01N
2900/1628 (20130101) |
Current International
Class: |
F01N
3/00 (20060101); F01N 3/20 (20060101); F01N
3/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
101779015 |
|
Jul 2010 |
|
CN |
|
102767437 |
|
Nov 2012 |
|
CN |
|
206346813 |
|
Jul 2017 |
|
CN |
|
102009024782 |
|
Feb 2010 |
|
DE |
|
102014209960 |
|
Dec 2014 |
|
DE |
|
2781893 |
|
Sep 2014 |
|
EP |
|
2781893 |
|
Sep 2014 |
|
EP |
|
2934011 |
|
Jan 2010 |
|
FR |
|
Other References
International Search Report and Written Opinion issued by the
ISA/US, Commissioner for Patents, dated Mar. 8, 2018, for
PCT/IB2017/056259; 6 pages. cited by applicant.
|
Primary Examiner: Largi; Matthew T
Attorney, Agent or Firm: Faegre, Drinker, Biddle &
Reath, LLP
Claims
We claim:
1. A diagnostic system, comprising: a sensor disposed downstream
from an exhaust gas aftertreatment system; and a central diagnostic
unit configured to diagnose a condensation condition associated
with the sensor for mitigating a sensor failure due to water
condensation on the sensor, the central diagnostic unit performing
the diagnosis on the condensation condition based on water storage
and release information related to a catalyst material of a
component of the exhaust gas aftertreatment system, such that the
sensor is activated based on the water storage and release
information.
2. The diagnostic system of claim 1, further comprising a virtual
dew point sensor configured to determine an estimated dew point
time and an estimated dew point temperature based on a water
release point of the component of the exhaust gas aftertreatment
system.
3. The diagnostic system of claim 2, wherein the sensor is
activated based on the estimated dew point time and the estimated
dew point temperature.
4. The diagnostic system of claim 2, wherein the estimated dew
point time and the estimated dew point temperature are variable
depending on a location of the sensor.
5. The diagnostic system of claim 2, wherein the water release
point is calculated by the central diagnostic unit based on a
kinetic model of the water condensation caused by the component of
the exhaust gas aftertreatment system.
6. The diagnostic system of claim 5, wherein the kinetic model is a
two-site kinetic model having a rate of adsorption and a rate of
desorption, both the adsorption and desorption rates associated
with the water condensation caused by the component of the exhaust
gas aftertreatment system.
7. The diagnostic system of claim 6, wherein the two-site kinetic
model includes a first model associated with the rate of adsorption
and a second model associated with the rate of desorption.
8. The diagnostic system of claim 1, wherein the sensor is a
nitrogen oxides sensor.
9. The diagnostic system of claim 1, wherein the sensor is disposed
downstream from a selective catalytic reduction (SCR) catalyst in
the exhaust gas aftertreatment system.
10. The diagnostic system of claim 1, wherein the component of the
exhaust gas aftertreatment system includes at least one of: an SCR
catalyst, a diesel oxidation catalyst, a diesel particulate filter,
and an ammonia oxidation catalyst device.
11. A diagnostic method for a sensor, comprising: disposing the
sensor downstream from an exhaust gas aftertreatment system;
performing a diagnosis on a condensation condition associated with
the sensor for mitigating a sensor failure due to water
condensation on the sensor; evaluating the condensation condition
based on water storage and release information related to a
catalyst material of a component of the exhaust gas aftertreatment
system; and activating the sensor based on the water storage and
release information.
12. The diagnostic method of claim 11, further comprising
determining a water release point based on an estimated dew point
time and an estimated dew point temperature associated with the
component of the exhaust gas aftertreatment system.
13. The diagnostic method of claim 12, further comprising
determining a safe activation point based on the water release
point of the component; and activating the sensor based on the safe
activation point.
14. The diagnostic method of claim 12, further comprising varying
the estimated dew point time and the estimated dew point
temperature depending on a location of the sensor.
15. The diagnostic method of claim 12, further comprising
calculating the water release point based on a kinetic model of the
water condensation caused by the component of the exhaust gas
aftertreatment system.
16. The diagnostic method of claim 15, further comprising
generating a two-site kinetic model having a rate of adsorption and
a rate of desorption, wherein both the adsorption and desorption
rates are associated with the water condensation caused by the
component of the exhaust gas aftertreatment system.
17. The diagnostic method of claim 16, further comprising
generating a first model associated with the rate of adsorption and
a second model associated with the rate of desorption for the
two-site kinetic model.
18. The diagnostic method of claim 11, further comprising including
a nitrogen oxides sensor as the sensor.
19. The diagnostic method of claim 11, further comprising disposing
the sensor downstream from a selective catalytic reduction catalyst
in the exhaust gas aftertreatment system.
20. The diagnostic method of claim 11, further comprising including
at least one of: an SCR catalyst, a diesel oxidation catalyst, a
diesel particulate filter, and an ammonia oxidation catalyst device
as the component of the exhaust gas aftertreatment system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national phase filing of International
Application No. PCT/IB2017/056259, titled SYSTEM AND METHOD TO
MITIGATE SENSOR FAILURES DUE TO WATER CONDENSATION, filed Oct. 10,
2017, the disclosure of which being expressly incorporated herein
by reference.
TECHNICAL FIELD
The present disclosure relates generally to systems and methods for
diagnosing sensor operation, and more specifically to a diagnostic
system and method for diagnosing operation of sensors in an exhaust
gas aftertreatment system.
BACKGROUND
Many exhaust systems use a catalyst and a sensor of some kind
downstream of the catalyst. In such systems, under certain
conditions water may be stored by and released from the catalyst,
condensing on the sensor and causing damage. For example, certain
diesel aftertreatment systems use a catalyst and a downstream
nitrogen oxides (NOx) sensor (e.g., in a vehicle tailpipe) which
can be damaged due to water condensation. Catalyst components,
especially Zeolite-based catalysts (e.g., Cu-Zeolite catalyst), can
store and subsequently release significant amounts of H.sub.2O
which can condense on the sensor. The condensation depends on many
factors in addition to the engine out H.sub.2O concentration.
Therefore, to avoid damage to the sensor, it is typically disabled
for a significant time during certain operating conditions that may
result in condensation (e.g., during cold start). This approach
results in disabling the NOx sensor for longer periods of time than
necessary, which results in undesirable periods of time when NOx is
not being monitored. This may result in reduced emissions control.
Accordingly, there exists a need to control the operational window
of such sensors to prevent operation during conditions under which
condensation can occur while broadening the operational window.
SUMMARY
According to one embodiment, the present disclosure provides a
diagnostic system, including a sensor disposed downstream from an
exhaust gas aftertreatment system; and a central diagnostic unit
configured to diagnose a condensation condition associated with the
sensor for mitigating a sensor failure due to water condensation on
the sensor, the central diagnostic unit performing the diagnosis on
the condensation condition based on water storage and release
information related to a component of the exhaust gas
aftertreatment system, such that the sensor is activated based on
the water storage and release information.
In one example, the diagnostic system further includes a virtual
dew point sensor configured to determine an estimated dew point
time and an estimated dew point temperature based on a water
release point of the component of the exhaust gas aftertreatment
system. In another example, the sensor is activated based on the
estimated dew point time and the estimated dew point temperature.
In yet another example, the estimated dew point time and the
estimated dew point temperature are variable depending on a
location of the sensor. In still another example, the water release
point is calculated by the central diagnostic unit based on a
kinetic model of the water condensation caused by the component of
the exhaust gas aftertreatment system. In still yet another
example, the kinetic model is a two-site kinetic model having a
rate of adsorption and a rate of desorption, both the adsorption
and desorption rates associated with the water condensation caused
by the component of the exhaust gas aftertreatment system. In a
further example, the two-site kinetic model includes a first model
associated with the rate of adsorption and a second model
associated with the rate of desorption.
In another example, the sensor is a nitrogen oxides sensor. In a
further example, the sensor is disposed downstream from a selective
catalytic reduction (SCR) catalyst in the exhaust gas
aftertreatment system. In a yet further example, the component of
the exhaust gas aftertreatment system includes at least one of: an
SCR catalyst, a diesel oxidation catalyst, a diesel particulate
filter, and an ammonia oxidation catalyst device.
According to another embodiment, the present disclosure provides a
diagnostic method for a sensor. The method includes the steps of
disposing the sensor downstream from an exhaust gas aftertreatment
system; performing a diagnosis on a condensation condition
associated with the sensor for mitigating a sensor failure due to
water condensation on the sensor; evaluating the condensation
condition based on water storage and release information related to
a component of the exhaust gas aftertreatment system; and
activating the sensor based on the water storage and release
information.
In one example, the method includes determining a water release
point based on an estimated dew point time and an estimated dew
point temperature associated with the component of the exhaust gas
aftertreatment system. In a further example, the method includes
determining a safe activation point based on the water release
point of the component; and activating the sensor based on the safe
activation point. In a yet further example, the method includes
varying the estimated dew point time and the estimated dew point
temperature depending on a location of the sensor. In a still
further example, the method includes calculating the water release
point based on a kinetic model of the water condensation caused by
the component of the exhaust gas aftertreatment system. In a still
yet further example, the method includes generating a two-site
kinetic model having a rate of adsorption and a rate of desorption,
wherein both the adsorption and desorption rates are associated
with the water condensation caused by the component of the exhaust
gas aftertreatment system. In a variation, the method includes
generating a first model associated with the rate of adsorption and
a second model associated with the rate of desorption for the
two-site kinetic model.
In another example, the method includes including a nitrogen oxides
sensor as the sensor. In yet another example, the method includes
disposing the sensor downstream from a selective catalytic
reduction (SCR) catalyst in the exhaust gas aftertreatment system.
In still another example, the method includes including at least
one of: an SCR catalyst, a diesel oxidation catalyst, a diesel
particulate filter, and an ammonia oxidation catalyst device as the
component of the exhaust gas aftertreatment system.
While multiple embodiments are disclosed, still other embodiments
of the present disclosure will become apparent to those skilled in
the art from the following detailed description, which shows and
describes illustrative embodiments of the present disclosure.
Accordingly, the drawings and detailed description are to be
regarded as illustrative in nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features of this disclosure and the
manner of obtaining them will become more apparent and the
disclosure itself will be better understood by reference to the
following description of embodiments of the present disclosure
taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a functional block diagram of a sensor diagnostic system,
featuring a central diagnostic unit;
FIGS. 2-7 illustrate exemplary diagnostic methods of the central
diagnostic unit of FIG. 1; and
FIG. 8 is a flow chart of an exemplary method of executing the
diagnostic methods of the central diagnostic unit of FIG. 1.
Corresponding reference characters indicate corresponding parts
throughout the several views. Although the drawings represent
embodiments of the present disclosure, the drawings are not
necessarily to scale and certain features may be exaggerated in
order to better illustrate and explain the present disclosure. The
exemplifications set out herein illustrate an exemplary embodiment
of the disclosure, in one form, and such exemplifications are not
to be construed as limiting the scope of the disclosure in any
manner.
DETAILED DESCRIPTION
Preferred embodiments of the present disclosure are described below
by way of example only, with reference to the accompanying
drawings. Further, the following description is merely exemplary in
nature and is in no way intended to limit the disclosure, its
application, or uses. As used herein, the term "unit" or "module"
may refer to, be part of, or include an Application Specific
Integrated Circuit (ASIC), an electronic circuit, a processor or
microprocessor (shared, dedicated, or group) and/or memory (shared,
dedicated, or group) that executes one or more software or firmware
programs, a combinational logic circuit, and/or other suitable
components that provide the described functionality. Thus, while
this disclosure includes particular examples and arrangements of
the units, the scope of the present safety control system should
not be so limited since other modifications will become apparent to
the skilled practitioner.
One of ordinary skill in the art will realize that the embodiments
provided can be implemented in hardware, software, firmware, and/or
a combination thereof. Programming code according to the
embodiments can be implemented in any viable programming language
such as C, C++, HTML, XTML, JAVA or any other viable high-level
programming language, or a combination of a high-level programming
language and a lower level programming language.
As used herein, the modifier "about" used in connection with a
quantity is inclusive of the stated value and has the meaning
dictated by the context (for example, it includes at least the
degree of error associated with the measurement of the particular
quantity). When used in the context of a range, the modifier
"about" should also be considered as disclosing the range defined
by the absolute values of the two endpoints. For example, the range
"from about 2 to about 4" also discloses the range "from 2 to
4."
As is further described below, the present disclosure includes the
development of a fundamental model to describe H.sub.2O adsorption
and desorption along with thermal effects on catalyst components
such as a Cu-Zeolite catalyst. The model is a kinetic model
developed from lab data and validated using engine data. The model
may be used to predictively determine operational boundaries to
mitigate sensor failures due to water condensation. Typical
approaches to sensor operation control limit the operational range
of the sensor to avoid condensation-induced cracking. Consequently,
using such conventional approaches the sensor is disabled for much
of the FTP cycle. Using the teachings of the present disclosure,
sensor failures due to water condensation may be mitigated while
the operational window of the sensor may be broadened compared to
conventional methods, thereby enabling compliance with in-use ratio
requirements established by the EPA.
Referring now to FIG. 1, a sensor diagnostic system 10 is shown
that performs diagnostic processes on one or more sensors of a
vehicle (not shown). As shown, system 10 generally includes a
diesel oxidation catalyst ("DOC") 12 positioned to receive exhaust
from an engine 14, a diesel particulate filter ("DPF") 16
downstream from the DOC 12, a selective catalytic reduction ("SCR")
catalyst 18 downstream from the DPF 16, a diesel exhaust fluid
("DEF") tank 20 that supplies DEF to a DEF valve 22 for
introduction into the exhaust stream between DPF 16 and SCR
catalyst 18, and a NOx sensor 24 downstream from the SCR catalyst
18. System 10 may further include a flow sensor 26 upstream from
DOC 12 which indicates the exhaust flow from engine 12 and a
temperature sensor 28 positioned to provide an indication of the
temperature of exhaust at the inlet of SCR catalyst 18. As is
further described herein, an engine control module ("ECM") or
controller 30 may be in communication with NOx sensor 24, flow
sensor 26 and temperature sensor 28 and configured to carry out an
analysis of the operating conditions of system 10 to determine when
to activate and deactivate NOx sensor 24.
As shown, controller 30 generally includes a processor 31 and a
non-transitory memory 33 having instructions that, in response to
execution by processor 31, cause processor 31 to perform the
various functions of controller 16 described herein. Processor 31,
non-transitory memory 33, and controller 30 are not particularly
limited and may, for example, be physically separate. Moreover, in
certain embodiments, controller 30 may form a portion of a
processing subsystem including one or more computing devices having
memory, processing, and communication hardware. Controller 30 may
be a single device or a distributed device, and the functions of
the controller 30 may be performed by hardware and/or as computer
instructions on a non-transient computer readable storage medium,
such as non-transitory memory 33.
Included in the processor 31 is a central diagnostic unit ("CDU")
35 configured to diagnose a condensation condition associated with
NOx sensor 24 and mitigate a sensor failure due to water
condensation on NOx sensor 24 using a virtual dew point sensor
("VDS") 37. In embodiments, CDU 35 is designed to mitigate the
sensor failure due to water condensation by determining when it is
likely safe to turn on NOx sensor 24. CDU 35 provides, among other
things, an approach to controlling NOx sensor operation by using
virtual dew point sensor 37 based on a kinetic model. VDS 37
determines operational boundaries of NOx sensor 24 for avoiding
potential condensation on the tailpipe NOx sensor 24. Moreover, it
is known that idle conditions can also result in water condensation
on NOx sensor 24 due to lower temperatures. VDS 37 is also useful
to develop strategies during idle conditions to avoid condensation
on NOx sensor 24. Thus, it is advantageous that CDU 35 is helpful
for increasing the robustness of NOx sensor 24 and broadening its
operational window.
While the present disclosure is described primarily in the context
of mitigating failures of NOx sensor 24 positioned downstream from
SCR catalyst 18, it should be understood that the teachings of the
present disclosure may be applied in various other systems. In
general, the present disclosure has application to any system
having a sensor susceptible to condensation damage positioned
downstream of a catalyst that stores water. Other suitable sensors
are also contemplated to suit different applications.
In certain embodiments, controller 30 includes one or more
interpreters, determiners, evaluators, regulators, and/or
processors that functionally execute the operations of controller
30. The description herein including interpreters, determiners,
evaluators, regulators, and/or processor emphasizes the structural
independence of certain aspects of controller 30, and illustrates
one grouping of operations and responsibilities of the controller.
Other groupings that execute similar overall operations are
understood within the scope of the present application.
Interpreters, determiners, evaluators, regulators, and processors
may be implemented in hardware and/or as computer instructions on a
non-transient computer readable storage medium, and may be
distributed across various hardware or computer based
components.
Example and non-limiting implementation elements that functionally
execute the operations of controller 30 include sensors providing
any value determined herein, sensors providing any value that is a
precursor to a value determined herein, datalink and/or network
hardware including communication chips, oscillating crystals,
communication links, cables, twisted pair wiring, coaxial wiring,
shielded wiring, transmitters, receivers, and/or transceivers,
logic circuits, hard-wired logic circuits, reconfigurable logic
circuits in a particular non-transient state, any actuator
including at least an electrical, hydraulic, or pneumatic actuator,
a solenoid, an op-amp, analog control elements (springs, filters,
integrators, adders, dividers, gain elements), and/or digital
control elements.
Certain operations described herein include operations to interpret
and/or to determine one or more parameters or data structures.
Interpreting or determining, as utilized herein, includes receiving
values by any method known in the art, including at least receiving
values from a datalink or network communication, receiving an
electronic signal (e.g. a voltage, frequency, current, or PWM
signal) indicative of the value, receiving a computer generated
parameter indicative of the value, reading the value from a memory
location on a non-transient computer readable storage medium,
receiving the value as a run-time parameter by any means known in
the art, and/or by receiving a value by which the interpreted
parameter can be calculated, and/or by referencing a default value
that is interpreted to be the parameter value.
As is understood by those skilled in the art, in system 10 exhaust
from engine 14 flows through DOC 12 where nitric oxide (NO O.sub.2)
is converted into NO.sub.2. The NO.sub.2 reacts with carbon in DPF
16 to produce CO.sub.2 and NOx. A mist of DEF is sprayed into the
diesel exhaust stream by DEF valve 22 to form ammonia (NH.sub.3)
through a series of reactions. The NOx and NH.sub.3 flow into SCR
catalyst 18 where they react to form N and H.sub.2O vapor, thereby
reducing the released emissions (NOx and NH.sub.3) to near-zero
levels.
In the present disclosure, methods and systems are disclosed for
predicting water concentration and temperature beyond SCR catalyst
18 (e.g., at NOx sensor 24) by modeling the adsorption and
desorption at SCR catalyst 18. As indicated above, SCR catalyst 18
can store significant amounts of water at low temperature, much of
which is released with higher temperature, which may cause damaging
condensation at NOx sensor 24.
Referring now to FIGS. 2-7, exemplary diagnostic methods of CDU 35
using VDS 37 are shown. In FIG. 2, CDU 35 utilizes data shown in a
plot 32 depicting the amount of water storage of a catalyst
material (such as SCR catalyst 18). Data set 34 of plot 32 shows
the water uptake characteristics of the catalyst at a temperature
of 76.degree. C. Each point 36 shows the water uptake (Y-axis)
after four hours of exposure to the water concentration indicated
by the X-axis. For example, as indicated by point 36, it is
determined that at 76.degree. C. and a water concentration of
approximately 6 mol %, the water uptake of the catalyst is
approximately 2.7% per unit mass of the catalyst. This is
determined by weighing the sample catalyst when dry (i.e., prior to
exposure to the water concentration), and then weighing again after
four hours. Data set 38 shows water uptake at a temperature of
51.degree. C. Data set 40 shows water uptake at a temperature of
25.degree. C. Similarly, data set 42 shows water uptake at a
temperature of 17.degree. C. As can be seen from the data, the
catalyst sample absorbed water much more readily at lower
temperatures.
Referring now to FIG. 3, the data depicted in FIG. 2 is reproduced
using a different X-axis (e.g., relative humidity percent). As
shown in plot 44 of FIG. 3, for all data sets 34, 38, 40, 42 there
is a rapid water uptake for water concentrations in region 46. In
region 48, actual condensation in the form of water droplets began
to occur. For concentrations between regions 46 and 48, water
uptake occurred without condensation.
Referring now to FIG. 4, during the diagnostic process, CDU 35
utilizes data shown in a plot 50 depicting the results of an
experiment of the dynamics of water storage and release in a sample
catalyst. Typically, the sample catalyst is placed in a reactor
tube and the gas concentration and temperature provided to the tube
is carefully controlled. Plot 50 includes water concentration of an
inlet gas 52, water concentration 54 of the sample catalyst and
temperature 56. During the adsorption phase of the experiment
(indicated by region 58 encompassing approximately the first 600
seconds), temperature is held constant at approximately 80.degree.
C. and gas having a water concentration of approximately 3% is
supplied to the reactor tube.
In certain cases, SCR catalyst 18 can store significant amount of
water at low temperature. At higher temperatures, the water can be
released as vapor. Even though engine out H.sub.2O concentration
may not exceed a dew point level, the additional water vapor
released by aftertreatment system components can exceed the dew
point level at the sensor location (which could be cooler than the
catalyst surface) and hence condense out the water and damage NOx
sensor 24. If engine out water is at 10%, the vapor release will
add to the water condensation, increasing the water concentration
to 15%. This can exceed the dew point level and lead to
condensation. Conventional diagnostic systems do not address this
additional stored water in the aftertreatment system components,
such as SCR catalyst 18, DOC 12, DPF 16, AMOX (ammonia oxidation
catalyst devices), or the like. For example, SCR catalyst 18 stores
a maximum amount of water that is up to 4 or 5 times more than that
of DOC 12.
When water is stored on SCR catalyst 18, it is an exothermic
process leading to significant heat rise. For example, an SCR out
temperature can be higher than SCR in temperature. During water
release, the opposite happens. SCR out temperature is less than SCR
in temperature. Further, there is added water from SCR catalyst 18.
These two factors are especially conducive to water condensation on
NOx sensor 24. In some cases, a temperature drop can be as much as
70.degree. Celsius (C) across two ends of SRC catalyst 18. For
example, if the temperature drop is another 20.degree. C. at the
tailpipe, this is a significant drop in temperature that can lead
to condensation.
As shown, sample water concentration 54 lagged inlet gas
concentration 52, and an area 60 between sample water concentration
54 and inlet gas concentration 52 represents the water that is
stored in the sample catalyst. Specifically, the sample catalyst is
saturated at the end of adsorption region 58. During the isothermal
desorption region 62, the inlet gas is switched off and the
temperature is held at approximately 80.degree. C. for
approximately one hour. During the temperature programmed
desorption phase of the experiment (indicated by region 64) thermal
desorption spectroscopy is used to observe desorbed molecules from
the surface of the sample catalyst as temperature 56 is increased.
As shown, as temperature 56 is ramped through approximately
150.degree. C., a small amount of water is released at a water
release point 66 (see an increase in sample water concentration 54)
demonstrating that a portion of the adsorbed water requires a
higher temperature for release.
VDS 37 is configured to determine an estimated dew point time and
an estimated dew point temperature based on the water release point
66. The estimated dew point time and the estimated dew point
temperature are variable depending on a location of NOx sensor 24.
In embodiments, if the exhaust gas temperature is below the
estimated dew point temperature, CDU 35 places NOx sensor 24 in a
deactivated state (e.g., turn it off if already turned on) during
cold idle, start-up time, cold ambient, cold start, etc. As such,
CDU 35 provides the ability to model the storage and release of
water on the catalyst surface. Conventional sensor diagnostic
systems do not take into account the water storage and release on
the aftertreatment system components.
In embodiments, CDU 35 determines a safe activation point 67 by
adding a predetermined time period 69 to the water release point
66, such that NOx sensor 24 is activated immediately after the
water condensation associated with NOx sensor 24 is less than a
predetermined threshold. As a result, NOx sensor 24 is activated
faster and earlier than conventional systems and thus CDU 35
provides enhanced NOx emission control. In conventional systems,
NOx sensor 24 is typically deactivated for a longer time period
during most of the cold start period because the water release
point 66 at the location of NOx sensor 24 is unknown. In contrast,
with CDU 35, NOx sensor 24 is activated earlier, causing fuel
efficiency benefits, and EPA in-use ratio requirements are met
faster since CDU 35 activates NOx sensor 24 earlier. As a result,
an operating window of NOx sensor 24 is broadened.
For example, NOx sensor 24 is turned on based on dew point
prediction which requires knowledge of water concentration and
temperature at the location of NOx sensor 24. In a conventional
system, the water concentration is obtained from exhaust. However,
as shown in FIG. 6, water concentration at SCR 18 outlet can be
higher than exhaust due to a release of stored water (see spikes
88, 90 in FIG. 6). This phenomenon is described in further detail
below. CDU 35 accurately predicts the dew point based on the water
storage effect on catalytic components of the aftertreatment
system.
Referring now to FIGS. 4 and 5, CDU 35 generates a plot 68 of a
two-site kinetic model of water concentration of a catalyst exposed
to gas having approximately 1% water concentration over time at
approximately 82.degree. C. More specifically, plot 68 shows
results 70 of a first model of weakly bound water and results 72 of
a second model of strongly bound water.
For each model component, the following rate expressions are used:
rate of adsorption=k.sub.adsC.sub.H2O(1-.theta.) and rate of
desorption=k.sub.des.theta.; where
.times..function..times..times..alpha..times..theta. ##EQU00001##
For the weakly bound model, E.sub.des=54 kJ/mol; A.sub.des=6.6e11;
and .alpha.=0. For the strongly bound model, E.sub.des=100 kJ/mol;
A.sub.des=2.04e13; and .alpha.=0.13. Theta is dimensionless water
stored on the catalyst compared to its capacity to store water. As
should be apparent from the foregoing, when theta is one, the
catalyst is saturated (i.e., no more adsorption can occur).
K.sub.ads is the rate constant for adsorption, which is independent
of temperature. K.sub.des is the rate constant for desorption,
which is a strong function of temperature. In embodiments, weakly
bound water is desorbed at a lower temperature. For example,
primarily weakly bound water is desorbed during isothermal
desorption, as shown in region 62 of FIG. 4. However, strongly
bound water is primarily desorbed at a higher temperature, as shown
in region 64 of FIG. 4. Using the above-described model, the water
concentration and temperature can be predicted at the location of
outlet of SCR catalyst 18. In some embodiments, there is a heat
loss between the outlet of SCR catalyst 18 and the location of NOx
sensor 24. Therefore, the temperature and concentration at the
location of NOx sensor 24 can be predicted using an empirical model
based on actual measurements. For example, the first model 70
corresponds to the end of adsorption region 58 shown in FIG. 4, and
the second model 72 corresponds to the water release point 66 shown
in FIG. 4.
Referring now to FIGS. 6 and 7, CDU 35 generates a graph 74 of
water concentration during a typical cold start FTP regulatory
cycle. During the cold start period (i.e., approximately 0 to 200
seconds), a significant amount water is stored on SCR catalyst 18
as shown by dotted line 76 of FIG. 6. This water storage is
accompanied by a large heat release. As a result, the temperature
increases sharply along the length of SCR catalyst 18 (see plot 78
of FIG. 7 showing simulated catalyst inlet temperature 80, catalyst
middle temperature 82 and catalyst outlet temperature 84). Finally,
when SCR catalyst 18 is sufficiently warm (e.g., beyond 500
seconds), the stored water is released creating spikes in water
concentration of SCR catalyst 18 as shown by dotted line 76 that
are beyond engine out water concentration 86 (e.g., see spikes 88,
90). These spikes can exceed dew point levels in the vicinity of
NOx sensor 24, depending on the temperature at the sensor location.
That temperature is influenced not only by the engine-out heat
propagation through the system, but also by the heat effects of
H.sub.2O storage and release.
Referring now to FIG. 8, an exemplary method or process of
executing diagnostic system 10 is illustrated. Although the
following steps are primarily described with respect to the
embodiments of FIGS. 1-7, it should be understood that the steps
within the methods can be modified and executed in a different
order or sequence without altering the principles of the present
disclosure.
The method begins at step 100. In step 102, CDU 35 initiates a
diagnosis on a condensation condition associated with NOx sensor 24
for mitigating a sensor failure due to water condensation on NOx
sensor 24. In step 104, CDU 35 evaluates the condensation condition
based on water storage and release information related to SCR
catalyst 18. As discussed above, the water storage and release
information is used to activate NOx sensor 24 during the cold start
period. In step 106, VDS 37 determines an estimated dew point time
and an estimated dew point temperature based on a water release
point of the sample catalyst in SCR catalyst 18. However, the
estimated dew point time and the estimated dew point temperature
vary depending on a location of NOx sensor 24. It is also
contemplated that the location of NOx sensor 24 is variable
depending on the application. For example, NOx sensor 24 is located
downstream from AMOX or engine 14. Other suitable configurations
are contemplated to suit different applications.
In step 108, CDU 35 generates a two-site kinetic model having a
rate of adsorption and a rate of desorption. Both the adsorption
and desorption rates are associated with the water condensation
caused by the sample catalyst in SCR catalyst 18. In step 110, CDU
35 generates a first kinetic model associated with the rate of
adsorption and a second kinetic model associated with the rate of
desorption for the two-site kinetic model. In step 112, CDU 35
calculates the water release point 66 based on the first and second
kinetic models of the water condensation caused by the sample
catalyst in SCR catalyst 18. In step 114, CDU 35 determines a safe
activation point 67 by adding the predetermined time period 69 to
the water release point 66, such that NOx sensor 24 is activated
immediately after the water condensation associated with NOx sensor
24 is less than a predetermined threshold.
In step 116, when the safe activation point 67 is reached in time
and temperature, control proceeds to step 118. Otherwise, control
proceeds to step 120. In step 118, NOx sensor 24 is activated,
e.g., by CDU 35. In step 120, if NOx sensor 24 is in an activated
state, NOx sensor 24 is deactivated, e.g., by CDU 35. However, if
NOx sensor 24 is already in a deactivated state, step 120 is an
optional step and no deactivation is performed. In some
embodiments, if NOx sensor 24 is in the deactivated state, CDU 35
prevents NOx sensor 24 from being activated until the safe
activation point 67 is reached. It is also contemplated that NOx
sensor 24 is activated based on the estimated dew point time and
the estimated dew point temperature. The method ends at step 122
which may include a return to step 102.
It should be further understood that, the connecting lines shown in
the various figures contained herein are intended to represent
exemplary functional relationships and/or physical couplings
between the various elements. It should be noted that many
alternative or additional functional relationships or physical
connections may be present in a practical system. However, the
benefits, advantages, solutions to problems, and any elements that
may cause any benefit, advantage, or solution to occur or become
more pronounced are not to be construed as critical, required, or
essential features or elements. The scope is accordingly to be
limited by nothing other than the appended claims, in which
reference to an element in the singular is not intended to mean
"one and only one" unless explicitly so stated, but rather "one or
more." Moreover, where a phrase similar to "at least one of A, B,
or C" is used in the claims, it is intended that the phrase be
interpreted to mean that A alone may be present in an embodiment, B
alone may be present in an embodiment, C alone may be present in an
embodiment, or that any combination of the elements A, B or C may
be present in a single embodiment; for example, A and B, A and C, B
and C, or A and B and C.
In the detailed description herein, references to "one embodiment,"
"an embodiment," "an example embodiment," etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art with the benefit
of the present disclosure to affect such feature, structure, or
characteristic in connection with other embodiments whether or not
explicitly described. After reading the description, it will be
apparent to one skilled in the relevant art(s) how to implement the
disclosure in alternative embodiments.
While the present disclosure has been described as having exemplary
designs, the present disclosure can be further modified within the
spirit and scope of this disclosure. This application is therefore
intended to cover any variations, uses, or adaptations of the
present disclosure using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this present disclosure pertains and which fall within the
limits of the appended claims.
Furthermore, no element, component, or method step in the present
disclosure is intended to be dedicated to the public regardless of
whether the element, component, or method step is explicitly
recited in the claims. No claim element herein is to be construed
under the provisions of 35 U.S.C. 112(f), unless the element is
expressly recited using the phrase "means for." As used herein, the
terms "comprises," "comprising," or any other variation thereof,
are intended to cover a non-exclusive inclusion, such that a
process, method, article, or apparatus that comprises a list of
elements does not include only those elements but may include other
elements not expressly listed or inherent to such process, method,
article, or apparatus
Various modifications and additions can be made to the exemplary
embodiments discussed without departing from the scope of the
present disclosure. For example, while the embodiments described
above refer to particular features, the scope of this disclosure
also includes embodiments having different combinations of features
and embodiments that do not include all of the described features.
Accordingly, the scope of the present disclosure is intended to
embrace all such alternatives, modifications, and variations as
fall within the scope of the claims, together with all equivalents
thereof.
* * * * *